allow creating custom ReactTextUpdate in ReactTextInputShadowNode subclasses

[vonovak]

Summary

Motivation is the same as in #24927 - when building a custom textinput (eg with rich text editing), one needs custom text processing logic. ReactTextInputShadowNode contains

react-native/ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactTextInputShadowNode.java

Line 211 in 6671165

public void onCollectExtraUpdates(UIViewOperationQueue uiViewOperationQueue) {

where an instance of ReactTextUpdate is created. For the custom use case, we'd like to just change the usage of spannedFromShadowNode() to our own implementation.

from there:
It's easy to subclass ReactTextInputShadowNode and override public void onCollectExtraUpdates() but the problem is that the method accesses private members. It also means overriding more code than necessary as we only care for spannedFromShadowNode().

Solution might be changing the members to protected, but that seemed weird because there are already setters for them. Creating getters also seemed weird, as we'd end up having unused getters hanging around.

So the second way which I find nicer is changing protected static Spannable spannedFromShadowNode(ReactBaseTextShadowNode textShadowNode, String text) to just protected since that will allow subclasses to override just this behavior.

Changelog

[Android] [Added] - allow custom spannedFromShadowNode in ReactTextInputShadowNode subclasses

Test Plan

this will work just the same